1. Field of the Invention
The present invention relates to a recording apparatus for performing recording on a recording medium. More particularly, the invention relates to a recording apparatus having means for detecting the sheet width of a recording medium.
2. Related Background Art
In conventional recording apparatuses, it is a general practice that recordings are performed accompanying the feeding operation of a recording sheet to the recording unit. At this juncture, the recording sheet of a given shape should be at a predetermined position for a normal recording as prerequisite. Whether this condition has been satisfied or not is determined by detecting the difference in the reflective density of the recording sheet and the platen which holds this sheet on the basis of the output level of a sensor of a reflective type and others in use for the purpose. Therefore, the presence of the recording sheet is discriminated by examining whether the output level of such a sensor exceeds a given threshold value or not.
As a method of the kind, there is, for example, disclosed in Japanese Patent Laid-Open Application No. 56-150556, an apparatus for detecting the sizes of recording sheets, in which the light emitting element and light receiving element are arranged to travel along a scale provided in the width direction of a recording sheet for detecting the sheet width.
There is also disclosed in U.S. Pat. No. 4,265,556 a structure such that a sheet width detecting scanner is mounted on a carriage having an ink head for the performance of the sheet width detections.
However, in the conventional sheet width detection, the threshold value is set at a predetermined level in advance for the fiducial sensor output to discriminate the presence of a recording sheet. Consequently, if the aforesaid level of the sensor output should be varied due to any characteristic difference of an individual reflective sensor and others or due to changes brought about by elapsed time or the like, the reflective density of the aforesaid recording sheet should be lower than the anticipated value, or the reflective density of the aforesaid platen should be higher than the anticipated value, there might be some cases that the area where the recording sheet is supposed to be present, that is the position of this sheet, is erroneously detected.